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Chemical vapor generation as a sample introduction technique for speciation analysis


Sample introduction has been identified as the "Achilles' heel" of atomic spectrometry. Many efforts have devoted to improve sample transfer efficiency and with it the detection power. Chemical vapor generation (CVG) is an important sample introduction technique, and is widely used for atomic spectrometry for its enhanced sensitivity and selectivity. Nonvolatile analytes can be transformed to volatile or semivolatile species through chemical reaction. The generated gaseous analyte compounds can be separated from the sample matrix by a gas-liquid separator and subsequently transferred to the detector i.e. ICP-MS for detection, largely eliminating spectral and non-spectral interferences caused by matrix elements.

Apart from these advantages, chemical vapor generation has also some drawbacks. Chemical vapor generation efficiency depends on the analyte species being present. For conventional trace element analysis this problem can be circumvented by appropriate sample preparation transforming all element species into a single species. However, this approach cannot be used for speciation analysis, for which analyte transformation during sample preparation has to be avoided.

Analyte species transformation then has to be done after separation of species on-line on the way to the detection system. Unfortunately adding reagents post-column to the eluate and pushing the eluate through a reactor for the species transformation is adding dispersion to the sample flow, reducing the sensitivity gain obtained by enhanced analyte transfer through vapor generation as well as the separation power by peak broadening.  

On the other hand, the vapor generation of only selective species can be used for an operationally defined fractionation of those species that can be volatilized against those than are not volatilized. Such selective vapor generation can then be used for binary speciation without any prior species separation by chromatography. In general, selectivity can be controlled to some extend by selecting reaction parameters such as pH and derivatizing agent. Examples of such methods are the determination of inorganic/organic mercury or inorganic/organic arsenic. The main advantage of such non-chromatographic speciation methods is the much simpler instrumentation and the higher sample throughput.

Michael Sperling

Related Reviews of the technique

Vapor generation for sample introduction
Mariusz Slachcinski, Modern chemical and photochemical vapor generators for use in optical emission and mass spectrometry, J. Anal. At. Spectrom., 34 (2019) 257-273. DOI: 10.1039/c8ja00383a

Selective vapor generation for binary speciation analysis:
Maja Welna, Anna Szymczycha-Madeja, Pawel Pohl, Non-Chromatographic Speciation of As by HG Technique—Analysis of Samples with Different Matrices, Molecules, 25 (2020) 4944; doi:10.3390/molecules25214944

Chemical vapor generation as an interface for coupling HPLC and atomic spectrometry
Yasin Arslan, Emrah Yildirim, Mehrdad Gholami, Sezgin Bakirdere, Lower limits of detection in speciation analysis by coupling high-performance liquid chromatography and chemical vapor generation, Trends in Analytical Chemistry, 30/4 (2011) 569-585. DOI: 10.1016/j.trac.2010.11.017

Further chapters on techniques and methodology for speciation analysis:

Chapter 1: Tools for elemental speciation
Chapter 2: ICP-MS - A versatile detection system for speciation analysis
Chapter 3: LC-ICP-MS - The most often used hyphenated system for speciation analysis
Chapter 4: GC-ICP-MS- A very sensitive hyphenated system for speciation analysis
Chapter 5: CE-ICP-MS for speciation analysis
Chapter 6: ESI-MS: The tool for the identification of species
Chapter 7: Speciation Analysis - Striving for Quality
Chapter 8: Atomic Fluorescence Spectrometry as a Detection System for Speciation Analysis
Chapter 9: Gas chromatography for the separation of elemental species
Chapter 10: Plasma source detection techniques for gas chromatography
Chapter 11: Fractionation as a first step towards speciation analysis
Chapter 12: Flow-injection inductively coupled plasma mass spectrometry for speciation analysis
Chapter 13: Gel electrophoresis combined with laser ablation inductively coupled plasma mass spectrometry for speciation analysis
Chapter 14: Non-chromatographic separation techniques for speciation analysis Chapter 19: Chemical speciation modelling

last time modified: May 12, 2023


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